1986 XR 600 Twin Carb Won't Start

15 replies to this topic
  • mrholshot

Posted December 04, 2004 - 05:45 PM


Hello, I just bought a 1986 XR 600. The bike is stock except for a Supertrapp. When I went to look at it it was 40° out and we couldn't kick start it, not a pop, even with eather. So, we pull started it and after a while it started to fire but took a while. We finally got it running but it smoked alot and ran like crap, although it would run as long as you kept the bike moving or kept into the throttle while sitting still. It would stall if you tried to let it idle. I pulled the plug out and changed it, still nothing. I then took both carbs and cleaned the pilot and mains, they didn't even look that bad. I noticed the bike didn't have an air filter on it and don't know how long it was run like that. It has ok compression by kicking it. Now when I spray either in it the bike will pop, run for just a split second and die. The guy claimed it kick started and ran fine 2 months ago and seemed very honest. The petcock flows fuel fine. Headlight lights up when you kick it. Could the rings be toast to the point where it won't start? I didn't take the chokes apart or mess with the mixtur screw. Could the bike possibly be very lean with no filter, cold weather, and the Supertrapp? Any help would be greatly appreciated.

  • Miker

Posted December 04, 2004 - 06:46 PM


Compression, spark, and fuel. That's all you need. It sounds like a fuel issue. If the rings were so bad you would be able to tell by moving the kickstarter with your hand The auto decompression system should only kick in some times so you should be able to rotate the engine slowly to get on the power stroke and feel some resistance. (Compression). Kick the bike over with the spark plug removed, plugged in and grounded. You should see good spark when you kick it over. If you have spark and compression the only thing left is fuel.. I would remove the plug on the side of the motor and the valve caps. Put the bike on TDC and check the valve clearance. If it is close to spec then you at least know there is not an issue with the cam timing. You may have a bike that has skipped a tooth on the timing chain but I doubt it.

  • XR250rdr

Posted December 04, 2004 - 07:15 PM


The stator is an issue on the older bikes too. Makes starting progressively worse.

But I'd work the fuel angle as much as you can first though.

  • firezwr426

Posted December 05, 2004 - 07:41 AM


how good is "ok compression"? I have an '84 xr500r and you can damn near stand on the kickstarter when it hits its compression stroke... just a thought though... not saying it is the problem, but maybe you should double check...I think the first thing to check when compression is low would be that the valves are seating all the way (not too tight), but by no means would I call myself a mechanic... just trying to suggest "maybes" Oh, and good luck with that new (old) pig.... hope she will run for you.... :cry:

  • mrholshot

Posted December 05, 2004 - 08:11 AM


Well, I'm 180lbs and there is NO way I can stand on the kickstarter without it going down. My brother said his 350X ATC kicks about as hard. Spark looked a little week on the old plug but I don't know. I will try and adjust the valves if I can and try to check cam timing. If the cam chain skipped a tooth would it loose compression because of the valves closing too late? If something is majorly wrong this thing it is getting sold. I'm not going to spend $1500 on a $1000 bike.

  • mrholshot

Posted December 06, 2004 - 01:40 PM



  • mrholshot

Posted December 06, 2004 - 08:51 PM


Well, I pulled the carbs back off and there looked to be a little debris in the bottom but not bad. I put a compression guage on it and managed to get up to 140 psi gradually but tried it again and it was having trouble building 100 psi so unhooked the decompression to make sure it wasn't sticking. Still didn't build much compression so I took the valve caps off and there was play on the exhaust side but not on the intake so I played with the adjustments, I loosened up the intakes until they were just touching and tightened down the nuts and it fired in 4 kicks and sounded ok. I took it for a ride and it wheelied in first but not second, low speed was a little rough and it started to sputter and idle rough, I figured the valves were getting tighter as the engine warmed up. I then pulled one cap off and could feel blow-by coming out so I figured that either the valves were too tight or that I might need the valves reground.

  • RingKingPin

Posted December 06, 2004 - 10:30 PM


A lapping of the seats would help for sure if your were getting blow by. Before doing that, try putting in the air filter. You might be suprised. If the bike has older gas, no filter, aftermarket exhaust and it's really cold outside, you could be running mighty lean. Get a filter or take some discs out :cry:

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  • roosterk0031

Posted December 07, 2004 - 07:57 AM


Replacing the stator in my 87 was the best thing I could do for starting, my spark with a new plug was so weak it was hard to see, lighting coil is different from the ignition coil, so headlight working doesn't mean the stator is still strong. I bought mine from Ricky Stator for $130 or so, you can rewind them yourself or have someone else do it, so a search for that. It still can be tough to kick start when 40 F out still, as for the smoke and tough to start even after pulling I think you just had if flooded and takes a while to clear the cylinder of the excess gas.

I'm 200lbs and can stand on my kickstarter without it falling, but I do have a fresh (300 miles) piston and valve job. David

  • zx7rye

Posted December 07, 2004 - 08:14 AM


I would adjust the valves to spec and leak that motor down before dumping anymore money into it. Leakdown will isolate issues pretty easily and give you a better idea of what you have to deal with. If it's fine, give the carb a good douching. Then check spark. If after all that, it doesn't fire...ask your wife to kick it....JK :cry:

  • don87xr600

Posted December 07, 2004 - 09:53 AM


Waste of time rewinding a '90 or older xr600 stator, not enough poles. start with a '91 or newer, that fit right in.

  • roosterk0031

Posted December 08, 2004 - 10:48 AM


Yeah I agree with Don, the newer stators have two poles for the ignition and 8? vs 4 for the lighting, I didn't care about the lighting, but 2 vs 1 seems better for the ignition. I had a very difficult time seeing my spark at times, not easy when doing it by yourself. David

  • pearblossomal

Posted December 08, 2004 - 09:32 PM


Yes, the pre-'91 XR stator is a weak link. Common trait is hard starting, check the resistence through the stator coil (not the light coil) from the connectors under the seat (see your book for specs, I forgot the numbers and wire color). If your's is bad you are money ahead replacing with a '91 and up stator, much more reliable. This would be any of the 83-84 XR500 and 85-90 XR600. Only difference will be the case grommet (larger for '91 up) on the harness which you can cut down with a razor blade.

  • firezwr426

Posted December 09, 2004 - 12:13 AM


let us know how it goes...

  • mrholshot

Posted December 14, 2004 - 07:53 AM


Cleaned the carbs and set the valves and it starts and runs now. Thanks for the help everyone.

  • beer_studd_76

Posted December 15, 2004 - 11:22 PM


1) clean carbs and fresh gas

2) check for air leaks

3) check for spark - if no spark A) replace plug :cry: check ignition coil C) check stator

if none of this works, sell the bike

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